Electromechanical transducer of the electrostrictive type



Oct. 1968 J. ADAMIETZ ETAL 3,408,514

ELECTROMECHANICAL TRANSDUCER OF THE ELECTROSTRICTIVE TYPE Original FiledMay 19. 1964 2 sheets"shee' Oct 1968 J. ADAMIETZ ETAL ELECTROMECHANICALTRANSDUCER OF THE ELECTROSTRICTIVE TYPE 2 Sheets-Sheet 2 Original FiledMay 19, 1964 United States Patent 3,408,514 ELECTROMECHANICAL TRANSDUCEROF THE ELECTROSTRICTIVE TYPE Josef Adamietz, Traubing, Germany, andDietwalt Thierbach, deceased, late of Traubing, Germany, by EmmaThierbach, heir, Munich, Germany, assignors to SiemensAktiengesellschaft, a corporation of Germany Original application May19, 1964, Ser. No. 368,716. Divided and this application Sept. 18, 1967,Ser. No. 675,269 Claims priority, application Germany, May 21, 1963,

S 85,316 15 Claims. (Cl. 310-82) ABSTRACT OF THE DISCLOSURE A transducerfor translating electrical oscillations into mechanical bendingvibrations or vice versa comprises essentially a bar, tuning fork orother elastic structure capable of bending vibrations at a naturalfrequency and defining a neutral fiber or axis between the compressingand tensioning forces due to the bending motions. The structure forms aslot, preferably on a lateral side of the straight bar, or on oppositesides of the bar, or between the tines of the tuning fork. One or moreelectrostrictive members with respective electrode coatings are disposedin the slots in transversely spaced relation to the neutral axis and arefirmly joined at both sides with the elastic vibrator structure.Electric conductor means are connected with the electrode coatings tosupply excitation voltage to, or take generated voltage from, thetransducer. Since the bendable structure is constituted by a singleintegral piece which is not fully subdivided by the slots or theelectrostrictive insertions, the transducer has increased mechanicalstrength.

Specification Our invention relates to an electromechanical transducerwhich, through small plates or blocks of electrostrictive materialprovided with electrically conducting coatings, is designed as atransducer for translating electrical oscillations into mechanicalbending vibrations and vice versa, such transducer being applicable, forexample, as an end vibrator of a multipart electromechanical filter, andin one of its more specific although not exclusive aspects the inventionrelates to improvements of electromechanical bending vibrators asdescribed and claimed in the copending application Ser. No. 368,716,filed May 19, 1964, of which the present application is a division,claiming the original U.S. filing priority of May 19, 1964, and a Germanpriority of May 21, 1963.

According to the invention described in the copending application, atleast one plate or block member of elec trostrictive material isdisposed between the neutral fiber or axis of a bending vibratorstructure and its outer perimetric surface, and an electric polarizationis impressed on the electrostrictive member in a direction perpendicularto the planes of the conductive coatings. The bending vibrator structureproper, consisting for example of steel or quartz glass, is interruptedand thus subdivided by the electrostrictive member consisting, as arule, of a ceramic material.

It is an object of the present invention to provide a transducer of thebending type that is particularly resistant to mechanical jarring orshock loads.

Another object of the invention is to improve electromechanicaltransducers, generally of the type briefly described above, so as togreatly increase the mechanical strength of the vibrator.

To achieve these objects, and in accordance With a feature of thepresent invention, we provide the bending vibrator structure of anelectromechanical transducer with a lateral slot and we dispose at leastone block or plate member of electrostrictive material, provided withexcitation electrodes, between the neutral axis of the structure and itsouter perimetric surface, an electrically insulating layer beinginterposed between at least one of the excitation electrodes and thebending vibrator structure.

According to another feature of the invention, we dispose two opposinglypolarized plate or block members of electrostrictive material separatedby an electrically conducting layer in the lateral slot of the bendingvibrator structure.

According to a further feature of the invention, a favorable design ofelectromechanical bending vibrators is obtained by providing thevibrator structure with two slots located at only one side of theneutral axis and disposing the electrostrictive members with theirexcitation electrodes in the slots, or by providing the bending vibratorstructure with respective slots on both sides of the new tral axis anddisposing respective electrostrictive members with the appertainingexcitation electrodes in the two slots.

According to still another feature of the invention, the bendingvibrator structure is constructed as a tuning fork resonator. In thiscase, the blocks or other members of electrostrictive material withtheir excitation electrodes are disposed between the two fork tines, orthey are disposed in a slot located in the base portion of the forkwhich interconnects the two fork tines.

In such tuning fork resonators, it is of advantage to dispose aplurality of electrostrictive members in the slot and to separate themby a spacer piece of electrically insulating material preferably quartzglass. 4

Electrical rnultipoles can be constituted with such electromechanicalbending vibrators by subdividing the electrostrictive block or platemembers with the aid of electrically conducting interlayers.

The plate or block members of electrostrictive material can be rigidlyattached in the slot of the vibrator structure simply by placing themembers under mechanical prestress between the slot walls, thus applyinga holding force of suitable magnitude.

The invention will be further described with reference to theaccompanying drawings illustrating embodiments of electromechanicaltransducer according to the invention by way of example. On the drawing:

FIG. 1 shows schematically a perspective view of a bar-type transducer;

FIG. 2 is an elevational view of the same transducer with a voltageapplied thereto;

FIGS. 3 and 4 are elevational views of two other embodiments oftransducers according to the invention;

FIG. 5 is an electrical equivalent circuit diagram relating to thetransducer illustrated in FIG. 4;

FIGS. 6, 7 and 8 illustrate additional modifications of the invention asapplied to tuning fork resonators;

FIG. 9 is a bar-type transducer, similar to that of FIG. 1 andillustrating a further modification; and

FIG. 10 is an elevational view of still another embodiment illustratingthe application of the invention to a vibrator utilizing the so-calledtransverse piezoelectric effect.

Referring to FIG. 1, there is shown a mechanical bending vibrator whichcomprises a continuous bar of steel provided with a slot 107 in whichthere is disposed a block or plate member 106 of an electrostriceiveceramic, for example lead zirconate. The axial end faces of member 106have metal coatings 108 and 109, preferably of silver. One of the silvercoatings is bonded to the adjacent slot face of the steel bar 105. Aplate 110 of electrically non-conducting material, such as quartz glass,is'interposed between the other silver coating and the bar 105 and fusedor otherwise bonded to both. In the vibration nodes 7 and 8 there areattached rigid metal wires or rods 11 and 12 which may serve forcoupling the vibrator with other bending vibrators such as those of amultipart filter, or for anchoring of the vibrator in a casing (notillustrated). A conductor wire 116 is soldered to the silver coating 109and extends to a terminal Another wire 117 is attached to the bar at thevibration node 8 and extends to a terminal 103. To eliminate undesirableeffects on the electrical quality of the vibrator, the wires 116 and 117are made of light and flexible material. ,A dot-and-dash line 13indicates the so-called neutral axis of the vibrator, which locates theplane between the compressive and tensile forces arising from thevibration.

FIG. 2 is an elevational view of the vibrator of FIG. 1, when analternating voltage U is applied to terminals 100 and 103. The arrow 118indicates an electric polarization impressed on the electrostrictivemember 106. This polarization, for example in the positive half-wave ofthe electric alternating potential, is oriented in the same direction asthe electric field, and in the negative half-wave of the voltage, isoriented in opposition to the field direction. Corresponding to thispolarization, the electrostrictive member 106 expands under theinfluence of the electric field. Since the vibrator consists of acontinuous steel body, the expansion of the block 106 causes bendingforces to be exerted on the vibrator, which is thereby bent in themanner schematically shown in FIG. 2. When the polarity of thealternating voltage U, applied to the terminals 100 and 103, reverses,the member 106 contracts, whereby the vibrator is bent in the oppositedirection, which vibration state is not represented by FIG. 2. If thefrequency of the alternating voltage U substantially agrees with thenatural frequency of the vibrator, the latter executes intensive bendingvibrations in rhythm with the applied alternating voltage, which aresymmetrical to a plane containing the vibration nodes 7 and 8.

The electrostrictive member 106 and also the plate of quartz glass, canbe secured in the vibrator by soldering. For this purpose, the quartzglass plate 110 as well as the ceramic member 106 are provided withmetal coatings. It is also possible to attach the members 106 and 110 byshrinkage in the steel bar 105, in which process the contraction inlength occurring during cooling of the steel bar 105 places both members106 and 110 under mechanical compression which is expediently soselected that an intimate connection of the members 106 and 110 with thesteel part is effected.

FIGS. 3 and 4 illustrate examples of vibrators in which the quartz glassor other electrostrictively inactive material used for the separation ofthe excitation electrodes, is substituted by an electrostrictivelyactive material.

The vibrator according to FIG. 3 consists of a continuous steel bar 105into which a slot 107 is milled. Rods attached to bar 105 in thevibration nodes 7 and 8 may serve for supporting the vibrator in itscasing, these rods and casing being ommited in the drawing. In the slot107 there are soldered two blocks 120* of elec trostrictive materialseparated by a silver coating 128. A conductor wire 131 connected to thesilver layers extends to a terminal 100. Another conductor wire isattached to the steel bar 105 in the vibration node 8 and extends to aterminal 103. The polarization of block 120 is parallel to the axis ofthe steel bar and opposed to that of the block 121, as indicated byarrows 124 and 125. When an alternating voltage U is applied toterminals 100 and 103 then, for example in the positive halfwave, bothblocks 120 and 121 expand under the effect of the electric field, whilein the negative half-wave they contract, whereby the vibrator is excitedto bending vibrations.

The example according to FIG. 4 is a further development of the vibratorillustrated in FIG. 3. In addition to the excitation system formed bythe ceramic blocks 120 and 121 described above, the vibrator of FIG. 4is provided with a further electrostrictively active system whichconsists of ceramic blocks 122 and 123. These are mounted in anotherslot 107 formed in the steel bar 105. The polarization of each block 122and 123 is parallel to the bar structure and opposed to that of theother block as is indicated by arrows 126 and 127. Between the blocks122 and 123 there is disposed a silver coating 129 to which is soldereda connecting wire 132 leading to a terminal 102'. The silver coating 128likewise is provided with a connecting wire 131 extending to a terminal100'; and an additional connecting wire 130 extends from the vibrationnode 8 of the steel bar to a terminal 103. When an input alternatingvoltage U, is applied to the terminals 100 and 103', the vibrator isexcited to bending vibrations in the manner previously described. Byreason of these bending vibrations, the blocks 122 and 123 are subjectedto expansions and contractions, and as a result of the piezoelectriceffect between the silver layer 129 and the steel bar 105 there isproduced an alternating voltage whose frequency agrees with thefrequency of the exciting voltage and which can be obtained at theterminals 102' and 103 as an output voltage U In the embodiment of FIG.4, the two electrostrictively active systems are disposed in offsetrelation to each other on laterally opposite sides of the neutral axisof the vibrator structure. Practically the same electrical propertiescan be achieved if the electrostrictively active systems are arrangedexactly opposite each other or if they are arranged only on one side ofthe neutral axis and spaced a suitable distance apart.

If the vibrator is operated as a bipole, as in FIGS. 1 to 3, itselectrical behavior corresponds to that of an equivalent circuit inwhich the impedance condition between the terminals 100 and 103 isrepresented by a series resonant circuit formed of an inductance L, acapacitance C and a loss resistance R, another capacitance beingconnected in parallel to this series circuit.

The electrical equivalent circuit diagram of a vibrator operated as aquadrupole (according to FIG. 4) is illustrated in FIG. 5. A shuntcapacitance C is connected across the input terminals 100' and 103'; inthe longitudinal branch there is disposed a series resonant circuitcomprising the inductane L, the capacitance C' and the loss resistanceR; and a shunt capacitance C is connected between the output terminals102 and 103'. There occurs between the terminals 102' and 103 an outputalternating voltage U if the natural frequency of the vibrator agrees atleast approximately with the frequency of the input alternating voltageU...

FIGS. 6 to 8 show bending vibrators in the shape of tuning forks. Theseare especially useful at relatively low frequencies at which the greaterconstructional length of a bar-shaped bending vibrator of equalfrequency may be undesirable.

The embodiment of FIG. 6 comprises two blocks 136 and 137 of anelectrostrictive ceramic between the tines of a tuning fork bendingvibrator 135, as indicated by arrows 139 and 140. Each block ispolarized in opposition to the polarization of the other. A silver layer138 separates the blocks 136 and 137, and a connecting wire 141 extendsfrom the layer to a terminal 100. Another connecting wire 144 isattached directly to the steel body of the tuning fork and extends to aterminal 103. Since there is a point in the' tuning fork base in whichvirtually no movement occurs, a supporting rod 142 for anchoring thetuning fork in a casing (not illustrated) is attached to the fork baseat this point. When an alternatin voltage is applied to the terminals100 and 103, the electrostrictively active blocks 136 and 137 aresubjected to expansions and contractions which, due to the rigidconnection of the blocks with the tuning fork tines, are transmitted tothe entire tuning fork. Thus the tuning fork is excited to vibrationswhen its natural frequency agrees at least approximately with thefrequency of the voltage applied at the terminals 100 and 103.

The tuning fork resonator illustrated in FIG. 7 corresponds generally tothat illustrated in FIG. 6, except that the electrostrictively activesystem is disposed in a slot 143 provided in the base or bight piecewhich interconnects the two fork tines.

Tuning fork resonators as illustrated in FIGS. 6 and 7 can be operatedonly as bipoles. A quadrupole characteristic, however, can be achievedwith a tuning fork resonator as illustrated in FIG. 8.

The base portion of the tuning fork 145 has a slot 152 in which twoelectrostrictive systems are accommodated. These comprise two blocks ofelectrostrictive material between which a spacer piece 153 ofelectrically non-conducting material, for example quartz glass, isdisposed. The mutually opposed polarization of the blocks may correspondto the directions of respective arrows 148 and 149. From a silvercoating 150 applied to the block 146 a connecting wire 154 extends to aterminal 100', and from the silver coating 151 applied to the block 147a connecting wire 155 extends to a terminal 102'. Another connectingwire 156 is attached directly to the steel part and extends to aterminal 103. A supporting rod 142 is attached to the neutral point ofthe tuning fork 145.

When an input alternating voltage U whose frequency agrees substantiallywith the natural frequency of the tuning fork is applied to terminals100' and 103', the latter executes bending vibrations in the rhythm ofthe applied alternating voltage. These vibrations cause theelectrostrictive block 147 to expand and contract. As a result, analternating voltage appears between the silver coating 151 and the steelstructure 145 and can be taken as output voltage from the terminals 102'and 103'. The tuning fork resonator illustrated in FIG. 8 thus operatesin accordance with the equivalent circuit diagram of FIG. 5. Virtuallythe same electrical relations are achieved if the electrostrictivelyactive systems and the spacer piece 153 are arranged between the twofork tines similar to those of FIG. 6.

The embodiment of FIG. 9 comprises a straight steel bar 105 with a slot107 in which there are mounted four successively disposedelectrostrictive plate members 160, 161, 162 and 163 separated from eachother by respective silver coatings 165, 166 and 167. A connecting wire168 extends from the silver coating 165 to a terminal 100'. From silvercoating 167 a connecting wire 169 extends to a terminal 102' and fromsilver coating 166 a connecting wire 170 extends to a terminal 103' towhich also connected another wire 171 which extends from the steel bar105. As a rule, the connecting wire 171 is soldered to the steel bar atone of the vibration nodes 7 or 8. Due to the connection through wires170 and 171, the silver coating 166 lies on the same electricalpotential as the steel bar 105 of the vibrator. Each two adjacent onesof the magnetostrictive plates are opposingly polarized as is indicated,for example by the arrows 173 to 176. An input alternating voltageapplied to terminals 100' and 103' generates between terminals 102 and103, in the manner previously described, an output alternating voltagewhenever the frequency of the input alternating voltage is substantiallytuned to the natural frequency of the bending vibrator.

A virbrator constructed according to FIG. 9 has the advantage, amongothers, that the steel bar requires only one slot, whereby themechanical strength of the vibrator is increased. Its electricalequivalent circuit diagram corresponds to the one represented in FIG. 5.In a further development of the vibrator illustrated in FIG. 9, therecan be arranged in the slot 107 an additional pair of electrostrictiveplates separated by a metal interlayer, whose electromechanical couplingfactor differs from that of the other plates. Such an arrangementpermits in a simple manner to obtain an additional signal voltage whichcan be used for the control of other devices.

The vibration excitation of the bending vibrator illustrated in FIG. 10is effected by the so-called transverse piezoelectric elfect. The steelbar 105 is provided with a slot 107 into which there is soldered anelectrostrictively active plate 180. The plate carries excitationelectrodes 181 and 182 in the form of silver coatings which areconnected by wires 183 and 182 to respective terminals and 103.

The polarization of the electrostrictive plate 180 is indicated by thearrow 184. The application of an alternating voltage to the terminals100 and 103 causes the plate 180 to expand and contract. This movement,because of the transverse effect, results in expansions and contractionsof the electrostrictive ceramic 180 in the direction of the mechanicalexpansion of the vibrator bar and thus excites the bar to bendingvibrations. The embodiment illustrated in FIG. 10 corresponds to abipole vibrator and can be extended by another system of the same typeinto a vibrator operating as an electrical quadrupole. Analogously, thisexcitation system can also be used in tuning fork type vibrators asexemplified by FIGS. 6 to 8 and is preferably employed when only narrowfilter band widths are required.

Changes may be made within the scope and spirit of the appended claimswhich define what is believed to be new and desired to have protected byLetters Patent.

We claim:

1. An electromechanical transducer comprising an elastic vibratorstructure capable of bending vibrations at a natural frequency andhaving a neutral bending axis, said structure having a slot which has adimension of depth extending transversely of said axis, anelectrostrictive member having opposite faces and respective electrodeson said faces, said member being disposed in said slot in transverselyspaced relation to said axis and firmly joined with both sides of saidslot in said structure, at least one of said electrodes being insulatedfrom said structure, and electric conductor means in electricallyconducting con nection with said electrodes.

2. In a transducer according to claim 1, said vibrator structure beingformed substantially of a single integral piece of elastic material andhaving an elongated shape, said slot being located generally in themiddle portion of said shape and extending inwardly from a lateral sideof said shape.

3. In a transducer according to claim 1, said vibrator structure beingformed substantially as a straight and elongated bar and having twolongitudinally spaced vibration nodes, said slot being located betweensaid nodes in longitudinally spaced relation to each of said nodes andextending inwardly into said bar from a longitudinal side thereof.

4. In a transducer according to claim 1, said vibrator structure beingformed substantially as a tuning fork having a base portion and twotines integral with said base portion, said slot being adjacent andparallel to said base portion.

5. In a transducer according to claim 4, said slot being constituted bythe space-between said two tines.

6. In a transducer according to claim 4, said slot being disposed insaid base portion at the side thereof facing away from said tines.

7. In a transducer according to claim 2, said two faces and electrodesof said electrostrictive member being substantially planar and extendingsubstantially in planes perpendicular to said neutral axis.

8. In a transducer according to claim 7, one of said electrodes beingconductively joined in said slot with said structure, and anelectrically insulating layer interposed in said slot between said otherelectrode and said struct-ure.

9. In a transducer according to claim 7, one of said electrodes beingconductively joined in said slot with said structure, and anotherelectrostrictive plate member joined face-to-face with said otherelectrode and interposed in said slot between said other electrode andsaid structure, said two members having electrical polarizations inrespective mutually opposed directions parallel to said axis.

10. In a transducer according to claim 2, said structure having twoslots in opposite sides of said shape respectively, two of saidelectrostrictive members being disposed in said respective slots andelectrically polarized in mutually opposed directions.

11. In a transducer according to claim 1, comprising a plurality of saidelectrostrictive members disposed in said slot in a sequence directionparallel to said axis, a spacer of electrically insulating materialbeing interposed between the respective electrodes of two sequentiallyadjacent ones of said members.

12. In a transducer according to claim 11, said spacer consisting ofquartz glass.

13. In a transducer according to claim 1, said two faces and electrodesextending substantially parallel to structure.

References Cited UNITED STATES PATENTS 3,024,429 3/ 1962 Oavalieri333-72 3,078,427 2/ 1963 Poschendieder 333-72 3,128,397 4/1964 Shinada3l0-9.8 3,131,320 4/1964 Shinada 3109.6 3,209,176 9/1965 Paley 310-9.13,354,413 11/1967 K0 3l0--9.6 3,198,970 8/1965 Kritz 310-9 6 J. D.MILLER, Primary Examiner.

